What is the best way to promote an on-line shop? The cheapest and most efficient way please?

We are trying to promote our On-Line shop throughout the UK and wondered if anyone has had good results and can offer some advise.

Ideally we would be looking for the best and most effecient way of doing this, with a minimal or no outlay. We have just started to promote the shop and therefore am looking for a way to promote it for free if possible.

Any ideas would be great
thanks

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).